1. Field of the Invention
The present invention relates to a method for detecting residues on a component and particularly on the surface of the component.
2. Discussion of Prior Art
Most components still have residues from the manufacturing after their production. These may be macroscopic or may comprise microscopic changes of the surface. In particular, the surfaces may be chemically contaminated. Depending on its planned use, the component must be freed of the contaminations and cleaned accordingly. However, the type of the contamination must be known beforehand for this purpose. The methods explained in the following are used in the prior art for testing the purity of component surfaces.
In a visual examination of the component with the bare eye, it is examined whether irregularities are recognizable on metallic, glossy surfaces. Depending on the spottiness of the component after the cleaning, it may be decided whether it must be cleaned once again or not. The surface is often not accessible to a visual examination in the interior of a hollow body, so that a visual examination is not possible.
When wiping off the surface (DIN 65078) using special media (papers, filter papers), it is checked whether particles remain adhering on the wiping medium. Wiping off the surface is only possible when the surface to be tested is accessible, however.
In a rapid test method using adhesive strips (“Tesa film test”), a transparent adhesive strip is stuck onto the component. When the adhesive strip is pulled off, dirt located on the surface (above all dust, metal dust, abrasions, chips) remain adhering to the adhesive strip. Subsequently, the adhesive strip is stuck onto a white background, so that the individual dirt particles are well visible, and are then counted under the microscope (number) or measured using a photometer (grayscale).
In the dissolving method in connection with a suitable chemical detection method, the contaminations on the surface are chemically dissolved. The solution may then be examined using a gas chromatogram, for example (EN ISO 9377-2). Alternatively, the solution may be evaporated in a rotation evaporator, for example, and the residue on evaporation is subsequently examined in a downstream method.
The components may be washed using 2-propanol, and subsequently the particles are counted. A disadvantage in this case is that lubricant solutions are not detected when they pass as real solutions into the 2-propanol. Undissolved lubricant escapes detection using the present invention as does particle counting.
In detection of contamination via wettability, the difference of the surface tension with a clean or contaminated surface is exploited (DIN 65079 (12/87), DIN 53364 (06/75), DIN EN 828 (01/98), QVA-Z10-57-00 (08/96)). Specifically, to detect the contamination on this basis, a Fettrot test, a measurement using test inks, a nigrosin test, a contact angle measurement, or the like may be performed.
It is a requirement in all of the methods cited up to this point that the surface to be tested is well visible or that a surface sample may be taken. The lubricant cleanliness of surfaces in the interior of hollow bodies therefore often may not be tested using these methods without further measures, because they are not accessible.
The quantity of contamination may be concluded by determining the weight difference between the cleaned and the uncleaned component (“weighing method”). However, this method is only advisable for small components, since only then may the weighing be performed precisely enough. In addition, the result of weighing is influenced, inter alia, by the ambient humidity and the degree of dryness of a component. Weighing methods are restrictedly suitable or unsuitable for wet components.
Many mineral oil products contain materials which fluoresce or display colors upon irradiation using UV light (ultraviolet). If the suspicion exists that the residues on the components comprise materials of this type, such a UV test may be used for detecting the contamination. However, the chemical composition of the lubricant limits the applicability of this method. The presence of a suitable measuring apparatus is also a requirement.
Clean sheet steel forms an adherent copper coating in acidic copper sulfate (CuSO4) solution (concentration approximately 25 g/l), since copper is the more noble metal. A discoloration may thus be observed in a copper sulfate test. It is to be clarified in the specific case whether this method may be applied with relatively noble steels. Because of the toxicity of copper ions and the possible influence on the tendency toward corrosion of the materials used in conductive connection to copper, copper sulfate is precluded for use in the drinking water system.
In the “Berlin blue test”, the component to be examined is laid in an indicator solution (Berlin blue) or has a droplet of this indicator solution dripped on it. If the surface colors blue, it is not passive. The “Berlin blue test” is based on the formation of chemical compounds which the clean steel surfaces form with iron. A color reaction occurs. However, this may be more difficult or impossible to observe on the inner surfaces of hollow components. The influence of a reaction of the material with iron (II) and iron (III) ions may restrict the applicability of the Berlin blue test, however.
In an electrolyte, electrochemical procedures, which may provide information about the state of the surface (active or passive), occur on a metallic conductive surface upon the presence of a current or voltage. In anodic polarization measurement, an electrolyte droplet is applied between component surface and counter electrode and a current source is connected between component and counter electrode. The time curve of the resulting voltage and the current flowing is recorded and is used as the basis for judging the surface state. Two method variations are differentiated the two electrode technique and the three electrode technique. The apparatus outlay required for performing the measurements is relatively large, however.
In particular residues in the form of nitrite layers are analyzed using glow discharge spectroscopy. However, only relatively thick layers in the μm range may be detected. Thin contamination layers in the nm range may only be detected with difficulty.
Only comparatively thick layers in the μm range may also be analyzed in comparison to other technologies using x-ray fluorescence analysis (XFA). Nitrite layers may be detected especially well using the method. However, only smooth surfaces may be analyzed using this method. The method is especially suitable for examinations in the measurement laboratory, it is unsuitable for testing components on location in production.
Contaminations in the nm range may be assayed using electron spectroscopy. However, it requires a high apparatus outlay which is reflected in the costs for the method. In production, methods of this type may typically not be performed routinely because of the high outlay.
This is also true for electron microscopy and atomic force microscopy (electron force microscopy), using which contamination layers in the nanometer range are also detectable. Electron and atomic force microscopy also requires a high apparatus outlay, which is reflected in the cost for the method. In production, methods of this type may typically not be performed routinely because of the high outlay.
Hydrocarbon chains on the surface of components may be determined quantitatively using carbon determination through oxidation. The components to be assayed are heated to temperatures from 200° C. to 800° C. in a furnace. The temperature required is a function of the dirt composition. The hydrocarbon chains of organic contaminants are decomposed and desorbed, the carbon bonding in the furnace with the oxygen-containing transport gas to form a CO/CO2 mixture. A conductivity measuring cell, in which the gas is admixed with sodium hydroxide (NaOH), is used for measuring the carbon content of the transport gas. It is possible to differentiate between different hydrocarbon chains by decomposition at different temperatures because of the differences in the carbon released.